In order to enhance the potential benefits of platinum therapy, efforts have been directed at increasing the outpatient dose of CBDCA. However, an intramural NCI study of a regimen of CBDCA, 800 mg/m2, with GM-CSF support, demonstrated that although GM-CSF did appear able to moderate the incidence of neutropenic fever, cumulative thrombocytopenia persisted as the major dose-limiting problem. PIXY321 is a novel, genetically- engineered hemopoietin which is composed of the protein chains of the human cytokines, IL-3 and GM-CSF, joined into a single molecule by flexible peptide linker sequence. Testing of PIXY321 in nonhuman primates has demonstrated that it can enhance both white blood count and platelet recovery after whole body radiotherapy. Both clinical and animal data indicate that prechemotherapy administration of GM-CSF may not only enhance the pool of CSF-responsive progenitors but can also induce a state of chemoprotection for bone marrow progenitors. Based on this effect of GM-CSF, it seems important to consider the evaluation of both the standard postchemotherapy use of PIXY321 and its prechemotherapy administration.